It is now well known that both viscous and elastic properties control the transport of mucus in the pulmonary system. Indeed many obstructive pulmonary diseases such as chronic bronchitis and cystic fibrosis are associated with abnormalities in these rheological properties. Results of research at the university have shown that the rheology of mucus is determinated by the behavior of the long-chain mucopolysaccharide molecules which act as though they are associated through polymer-polymer interactions. These interactions may be interpreted as temporary, or transient, crosslinks. Abnormal mucus shows evidence of being far more tightly coupled (or crosslinked) than normal material. It was further established, however that the rheology of mucus can be changed drastically by changing ionic strength and pH. It will be shown in this proposal that these changes must be due to changes in specific polymer-polymer interactions such as hydrogen bonds or ion-pair coupling, however their origin is unknown. It is the purpose of the proposed research to identify these interactions and quantify their effect on mucus rheology by studying aqueous solutions of polymers with functional groups found in pulmonary secretions. Knowing the nature of these interactions will be invaluable in the search for mucolytic agents (and indeed even systemic treatment) to correct the abnormal behavior demonstrated by cystic and bronchitic mucus.